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ACPI video: work-around BIOS AML bug in _BQC 

_BQC on some laptops returns an uninitialized value when it's
invoked for the first time.

Set the laptop to the maximum backlight level in this case.
http://bugzilla.kernel.org/attachment.cgi?id=22675

Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>
This commit is contained in:
Zhang Rui 2009-08-31 12:39:54 -04:00 committed by Len Brown
parent 4a703a8fe5
commit 90c53ca426
1 changed files with 14 additions and 4 deletions
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18
drivers/acpi/video.c
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@ -878,7 +878,7 @@ acpi_video_init_brightness(struct acpi_video_device *device)
br->flags._BCM_use_index = br->flags._BCL_use_index;
/* _BQC uses INDEX while _BCL uses VALUE in some laptops */
br->curr = level_old = max_level;
br->curr = level = max_level;
if (!device->cap._BQC)
goto set_level;
@ -900,15 +900,25 @@ acpi_video_init_brightness(struct acpi_video_device *device)
br->flags._BQC_use_index = (level == max_level ? 0 : 1);
if (!br->flags._BQC_use_index)
if (!br->flags._BQC_use_index) {
/*
* Set the backlight to the initial state.
* On some buggy laptops, _BQC returns an uninitialized value
* when invoked for the first time, i.e. level_old is invalid.
* set the backlight to max_level in this case
*/
for (i = 2; i < br->count; i++)
if (level_old == br->levels[i])
level = level_old;
goto set_level;
}
if (br->flags._BCL_reversed)
level_old = (br->count - 1) - level_old;
level_old = br->levels[level_old];
level = br->levels[level_old];
set_level:
result = acpi_video_device_lcd_set_level(device, level_old);
result = acpi_video_device_lcd_set_level(device, level);
if (result)
goto out_free_levels;